1. Technical Field
The invention relates to tire building drums, and more particularly, to a first stage tire building drum for run flat tires having a central spacer which forms a pair of adjacent recesses for accommodating elastomeric inserts which form the elastomeric crescent shaped inserts in the sidewalls of run flat tires.
2. Background Information
Various tire constructions have been devised over the years which enable a tire to run in an under-inflated or non-inflated condition, such as after receiving a puncture and loss of pressurized air, for extended periods of time and at relatively high speeds. This enables the vehicle operator to safely drive the vehicle to an appropriate location for repair or replacement of the punctured tire. Certain of these safety tires, referred to as xe2x80x9crun flat tiresxe2x80x9d, have been successful for certain applications and certain types of tire constructions. Most of these run flat tires achieve their run flat capability, by the placement of reinforcing layers or crescent shaped members of a relatively stiff elastomeric material in the side walls of the tire which enable the tire to support the vehicle weight even with the complete loss of internal air pressure. Examples of such sidewall inserts are shown in U.S. Pat. Nos. 3,911,987; 3,949,798; 3,954,131; 4,067,372; 4,202,393; 4,203,481; 4,261,405; 4,265,288; 4,287,924; 4,365,659; 4,917,164; and 4,929,684.
However, problems develop when manufacturing such run flat tires having the sidewall inserts when using usual fabrication equipment and techniques due to the extreme care that must be taken to prevent air from being trapped between the uncured tire components and the creating of undesirable bulges and projections in the tire, without excessively increasing the cost of tire manufacture. This problem was recognized and was attempted to be solved by the forming of spaced depressions, in a specially constructed tire building drum for receiving the uncured material to form the sidewall inserts as shown in U.S. Pat. No. 5,591,288. However, this required constructing a special drum for receiving the rubber inserts and is limited to a particular size of tire produced thereby due to the size and location of the recesses in which the inserts are installed. Also, if the inserts are wider than the grooves they may ride out of the grooves creating a uniformity problem.
The present invention provides a first stage run flat tire building drum and method using a spacer or sleeve mounted on the center of a usual tire building drum, wherein the spacer has a width the same as the distance between the inside edges of the inbound and outbound sidewall rubber inserts of a run flat tire and a height equal to that of the rubber insert at its thickest point.
The tire building drum of the present invention enables the building of a uniform first stage tire carcass free of interruptions from the sidewall inserts and which provides a relatively smooth body contour for receiving the other tire components.
The tire building drum of the invention enables the inner liner to be placed radially inwardly or outwardly of the sidewall inserts without changing the structure of the tire building drum and without special assembly procedures.
Another aspect of the invention includes forming the spacer sleeve in same number of arcuate segments as is the expandable tire building drum so as to be compatible therewith, and in which the spacer segments can be formed of a rigid, lightweight material such as polyurethane.
Another feature of the invention is to provide building the first stage body ply without trapping air between the plies and inserts and without bumps or protrusions being formed thereby.
A further advantage of the invention is to enable a usual first stage tire building drum to be usable for building various sizes of run flat tires, having various size sidewall inserts, by changing the axial length and height of the spacer sleeve placed on the tire building drum, and without changing the method of manufacture of the first stage body ply carcass.
The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings.